I agree with frankthedolphintrainer! Geez you coul've picked a shorter name!! hehe.

I'm confused about how the open style round chambered head will raise compression ratio. It will if you shave it down a heap, but otherwise it has a much larger combustion chamber. I sat both styles on my bench for comparo. The open style head appears to be almost exactly the same except someone has come along and milled a heap of metal out of the chamber to reduce the compression.

Someone told me they did this for some engines, destined for countries with tight pullution control. The little A-series engine had been around for many years by this time and wasn't up to the challenge without modification. The reduced temperatures are apparently responsible for reduced nitricoxide gas emmisions, or was that sulpher something or other gas ?? Can't remember now, but it seemed like a reasonable story to me at the time and I've never doubted it.